1. Field of the Invention
The present invention relates to an electrochromic element, an optical element constituted of an electromotive force generating element for generating an electromotive force according to an intensity of an electromagnetic wave, and the aforementioned element, and a photographing unit equipped with such optical element.
The present invention relates to an electrochromic element having an electrochromic material capable of electron exchange on a surface of a nanoporous semiconductor, an optical density changing element having such electrochromic element, an optical element constituted of an aforementioned element and an electromotive force generating element, and a photographing unit equipped with such optical element.
2. Description of the Related Art
An element showing a change in an optical density in response to an electromagnetic wave has a wide field of application. As a material having a function of changing the optical density, namely controlling a light transmission or a light reflection in response to an electromagnetic wave, there are known a photochromic material and an electrochromic material.
The photochromic material is a material capable of changing an optical density thereof in response to a light irradiation, and is applied to sunglasses, an ultraviolet checker, printing-related materials, processed fiber products and the like.
The electrochromic material is a material capable of changing an optical density thereof in response to an electron injection or an electron ejection, and is applied to an antiglare mirror for automotives, an automotive window material and the like.
The application of such optical density changing material includes a photographing system, including a camera. For example, a film with lens is recently popular, because of its simplicity in operation, as a camera unit not requiring a film loading operation and enabling a photographing operation immediately after purchase. However the prior film with lens is not provided with a mechanism for regulating an exposure amount, as it is designed for simplicity. Therefore, a film with lens, loaded with a high sensitivity film, results in an excessive exposure in a photographing operation in a bright environment, thus often generating a failed whitish picture. Therefore, a film with lens capable of automatic switching of a diaphragm according to the light amount at the photographing, utilizing an AE control by a light metering in the photographing operation, has been commercialized. This has significantly reduced the photographing failure caused by the excessive exposure amount.
For realizing a “light regulating filter” for regulating the incident light amount to a photosensitive material, according to the light amount at the photographing operation, in a simple and inexpensive manner, there is proposed a film with lens utilizing the aforementioned photochromic material (for example JP-A No. 5-142700, JP-A No. 6-317815 and JP-A No. 2001-13301). More specifically, a photochromic material means a material having a property for developing a color or increasing an optical density when subjected to a light irradiation of a certain wavelength, and extinguishing the color or decreasing the optical density when the light irradiation is terminated or when subjected to heating or a light irradiation of a different wavelength, and such property is known in inorganic compounds containing silver halide and in a part of organic compounds. A light regulation is considered possible by positioning a filter, formed by a photochromic material, on an optical axis and executing color development and color erasing according to the incident light amount.
However, the photochromic compound generally requires about 1 minute for the color development and about several tens of minutes for color erasing (cf. Solid State and Material Science, 1990, Vol. 16, p. 291), and is therefore difficult to employ as a light regulating system for a photographing light.
On the other hand, the aforementioned electrochromic material is known to be capable of faster color development and color erasing. More specifically, the electrochromic material means a material having a property of increasing an optical density by an electron injection or an electron ejection under a voltage application, and decreasing the optical density by an electron transfer opposite to that at the increase of the optical density, and such property is known in certain metal oxides and organic compounds. A “light regulating filter” capable of regulating the incident light amount to the photosensitive material according to the light amount at the photographing operation can be realized by combining such electrochromic material with a power source and a light sensor for detecting the photographing light amount.
A light regulating system, laminating a solar cell generating an electromotive force in response to a light with an electrochromic material, is proposed (for example JP-A No. 9-244072). An automatic light regulation according to the light can be expected also in this system. However, in such proposed structure where the solar cell and the electrochromic material are superposed, a part of the light passing through the electrochromic material is inevitably absorbed by the solar cell, and such structure is therefore unsuitable for a system of a camera-related optical element in which it is desired to utilize the incident light amount to the photorecording medium as maximum as possible in a scene not requiring such light regulation.
On the other hand, an increase in the response speed is reported in an electrochromic material adsorbed in a porous layer of titanium oxide or antimony-doped tin oxide (for example JP-T No. 2000-506629, Solar Energy Materials and Solar Cells, 1998, Vol. 55, p. 215 and Journal of Physical Chemistry B, 2000, Vol. 104, p. 11449).
In case of utilizing an electrochromic element (optical density changing element) as a light regulating filter, a hue of the electrochromic element in a colored state is important. For example, in case of mounting a light regulating filter on a film with lens and regulating the light amount entering the film with lens, there is preferred an electrochromic element having a color hue close to a spectral sensitivity of a photographing film (for example a color negative film) loaded in the film with lens. In case the hue of the electrochromic element in the colored state is significantly different from the spectral sensitivity of the photographing film (for example a color negative film), a photograph obtained by an ordinary photographing processing shows a perturbed color balance, thus becoming a failure. In the prior technology, there has not been known an electrochromic element capable of showing a spectral sensitivity close to the spectral sensitivity of the photographing film.
It is reported that two types of such electrochromic material, adsorbed on a nanoporous semiconductor (such as titanium oxide or antimony-doped tin oxide) layer to constitute a set of electrodes (anode and cathode) and used in a mutually opposed relationship across an electrolyte, function as an optical density changing element of a high response speed (cf. JP-T No. 2000-506629, JP-T No. 2003-511837 and Journal of Physical Chemistry B, 2000, Vol. 104, p. 11449.).
It is investigated to utilize an optical density changing element in combination with a photosensor as a light regulating filter for photographing purpose. A use of a camera in an excessively bright location results in a failed photographing, but such failure can be prevented by an “automatic light regulating filter” in which a sensor, detecting a brightness at the photographing operation, sends an electric power to the optical density changing element to develop a color therein. For realizing such light regulating filter for photographing purpose, it is necessary to suitably utilize electrochromic materials showing color development at arbitrary wavelengths and having a fast response according to the purpose of photographing.